1. Field of the Invention
The present invention relates to well completion methods. More specifically, the present invention relates to an apparatus and method for assembling a wellscreen for use in oil, gas, and water wells.
2. Description of the Related Art
Wellbores are typically formed by drilling a borehole into the earth in order to penetrate one or more hydrocarbon-bearing formations. Typically, the wellbore is supported by one or more strings of steel casing which extend from the surface to a desired depth. An annular area is created between the casing and the borehole, which is filled with cement to further support and form the wellbore.
Some wells are produced by perforating the casing of the wellbore at selected depths where hydrocarbons are found. Hydrocarbons migrate from the formation, through the perforations, and into the cased wellbore. In some instances, a lower portion of a wellbore is left open, that is, it is not lined with casing. This is known as an open hole completion. In that instance, hydrocarbons in an adjacent formation migrate directly into the wellbore where they are subsequently raised to the surface, either by production pressure or through an artificial lift system.
One problem typically encountered in connection with production of downhole fluids is the invasion of aggregate material, including sand, into the wellbore. Sand production can result in premature failure of artificial lift and other downhole and surface equipment. Sand can also build up in the tubing to obstruct well flow. In addition, produced sand becomes difficult to handle and dispose at the surface.
The need to remove aggregates from production fluids exists in many types of wells, including oil and gas wells, water wells, geothermal wells, and wells for ground remediation. Typical particulates needing to be filtered out are sand and clay including unconsolidated particulate matter, also known as xe2x80x9cformation sandxe2x80x9d.
To control particle flow from unconsolidated formations, well screens are often employed downhole. These well screens serve as subterranean particle filters, and are conventionally referred to as xe2x80x9csand screens.xe2x80x9d Sand screens have been utilized in the petroleum industry for some time to remove particulates from production fluids.
Sand screens are typically tubular in shape and serve as a filtering barrier between a formation and a string of tubing or production equipment. Modern sand screens are typically constructed from three composite layers. These include a perforated base pipe, at least one porous filter media wrapped around and secured to the base pipe, and an outer cover. The filter media allows hydrocarbons to invade the wellbore, but filters sand and other unwanted particles from entering.
The sand screen is connected to the lower end of either the casing or the production tubing. Hydrocarbons travel to the surface of the well through the sand screen and via the tubing. Thus, hydrocarbons or other production fluid are filtered before entering the production string and before traveling through expensive production and pumping equipment.
A typical method of constructing a wellscreen involves wrapping and seam-welding mesh layers of filtering material around the perforated base pipe. The mesh layers typically consist of sintered mesh filter elements and more coarse wire mesh drainage elements. An alternative method involves forming a tube of the mesh material, seam welding it longitudinally, and then sliding it over the perforated base pipe. A protective outer shroud consisting of a perforated tube is then placed over the mesh layers and the perforated base pipe.
FIG. 1 shows a previous version of a perforated base pipe 12 for a prior art well screen 10. The base pipe 12 defines a tubular body having a plurality of perforations 14 therein. The base pipe 12 includes a central bore extending from a first end 20A to a second end 20B. At each opposite end 20A, 20B of the base pipe 12 is a termination member 16. Each termination member 16 defines a series of concentric step-tiered rings 22 having progressively larger diameters. As shown in FIG. 2, the step-tiered rings 22 of the prior art serve as support members for layers of filter screen 24 and the protective shroud (not shown) which will encompass the base pipe 12 upon completion of the well screen 10.
A disadvantage to known well screens 10 is the cumbersome manufacturing process. To assemble the wellscreen 10, the step-tiered rings 22 of the prior art perforated base pipe 12 (FIG. 1) require that the layers of filter screen 24 (shown in FIG. 2) be individually sized to fit each sequential tier on the termination members 22. This means that each layer of filter screen 24 must be cut in separate pieces in accordance with the specific diameter of each corresponding step ring 22. After being cut, the layers of filter screen 24 must be separately welded to each corresponding step ring 22, starting with the smallest diameter ring 22xe2x80x2 located at the base of the termination member 16, and moving up sequentially to each successively larger diameter ring 22 until the step ring having the largest diameter 22xe2x80x3 has been fitted for a layer of filter screen 24. This process results in many individual sections of mesh material 24 being separately cut and welded to the corresponding step-tiered rings 22 of the termination members 16.
FIG. 2 depicts an intermediate layer of filter media 22 being applied to a step ring 22 of a prior art base pipe 12. The step is repeated for each step ring 22. Thus, in the manufacturing process of the prior art, a plurality of layering and welding steps are required. These numerous steps represent a labor-intensive process that is both expensive and time consuming. In addition, this process also requires a greater degree of skill from the technicians in manufacturing and maintenance.
Therefore, a need exists for a perforated tubular that enables quicker and easier fabrication welding of filter screen layers to the step rings. There is a further need for a well screen that enables the filter layers to be prepared offline for easier assembly at the shop or well site. In addition, there is a need for a method for assembly of the filter screen layers onto a helical step-tiered surface in one continuous feed welding operation.
Further yet, there is a need for a method of manufacturing a sand screen which is less expensive, and which requires less time to manufacture, assemble, and maintain than known sand screens.
The present invention first relates to an improved filtering device for filtering particulates from fluid. In the preferred embodiment, the apparatus serves as a wellscreen for filtering sand and other aggregates during production of hydrocarbons from a downhole formation.
The wellscreen first comprises a perforated base pipe. At each opposite end of the base pipe is disposed a frustoconical termination member. The termination member includes a helical step-tiered surface, which serve as a support for an intermediate filtering media for the wellscreen. Thus, unlike the individual step-type rings of the prior art, the present invention offers an outer spiraling surface. In accordance with the present invention, the spiraled step surface forms a continuous helical pattern, allowing the filtering media to be spooled and attached onto the termination members during manufacturing. Thereafter, an outer protective perforated shroud may optionally be added.
The present invention also relates to a method for assembling a wellscreen. A pre-slotted base pipe is utilized as the base member for the wellscreen fabrication. As described above, a frusto-conical termination member is disposed at each opposite end of the base pipe. The termination member includes a spiraled step surface, which serves as a support surface for an intermediate filtering layer for the wellscreen. In accordance with the present invention, the spiraled step surface forms a continuous helical pattern, allowing a filtering media to be dispensed and attached onto the termination members in a single roll.
The base pipe, including the opposite termination members, is positioned onto a spool. The filtering layer is then cut and fed through a tensioning roller and attached onto the smallest diameter of the termination members. Thereafter, the spool is rotated so as to roll the filtering media onto the tiers of the termination members.
An outer protective perforated shroud may optionally be added to the base pipe and filtering media. The filtering media and the outer shroud are preferably welded onto the termination members to form a secure containment for the base pipe.
The completed wellscreen is designed to serve as an inlet port for production fluids in a downhole wellbore. Accordingly, the wellscreen is positioned in series with a string of production tubing or, in an open-hole completion, a string of casing, downhole. The wellscreen thus defines a multi-layered tubular, allowing fluids to be filtered and to enter production tubing. In one embodiment, the wellscreen includes a threaded pipe section at least one end to facilitate the fluid connection of the wellscreen to the production tubing.